Pharmacokinetics of Theophylline and 3‐Methylxanthine in Guinea Pigs. I. Single Dose Administration

: Aminophylline in the doses 6.31 · 10−5mol kg−1 and 2.37 · 10−4mol kg−1 (corresponding to 13.8 and 52.0 mg kg−1 respectively) and 3‐methylxanthine 2.37 · 10−4 mol kg−1 (39.4 mg kg−1) was administered to guinea pigs by intravenous bolus injection, n = 7, 10, and 6, respectively. The shape of semilogarithmic plots of all measured plasma theophylline concentrations versus time was compatible with the use of an open 2‐compartment pharmacokinetic model assuming first‐order distribution and elimination processes, but in the comparison of the mean values of the pharmacokinetic parameters obtained after the administration of the low and the high theophylline dose, statistical analysis by Student's t‐test showed β and V1 to be significantly altered (low dose: β=0.00338 min.−1, V1 = 392 ml kg−1; high dose: β = 0.00198 min.−1, V1 = 528 ml kg−1; P